that doesn't even make sense, that's exactly WHY people move their stamps to the new passport, the stamp transfer notes how you originally entered, how long you've been on extensions, your most recent entry to thailand and the current extension
if your current extension is from the immigration office where you live (like you said it is) then you just go to the immigration office there to move the stamps, No need to go back to where ever you started the Non-O first extension process
At Chaengwattana it is definitely free, BUT if you're moving stamps and you have an extension based on retirement, you need to update your bank book and give them a copy to get the stamps moved 😮
okay, if you've got all the documents required, AND you fill out the online application correctly, upload what's needed in the required fields, submit the application, get the confirmation <- PRINT the confirmation then go to the consulate and pay in cash for the visa you should get approved in 3 - 4 days max.
"Regular visas" (Non-O, Non-B, Non-ED) applications go pretty fast.
Just make sure you go slow, get the uploads correct, check the data entry to make sure there's no mistakes BEFORE you submit it. Most of the reports of them taking a long time are self inflicted because people didn't check their application carefully before submitting it and they had to get emailed for more documents
If you're not going to get the extension you can stay the 90 days the initial stamp gave you and leave when you want (obviously before that stamp runs out), It'll 'cancel' when you leave the country.